Pump

ABSTRACT

To provide a pump capable of discharging gas bubbles and thus maintaining a discharging ability, even when the gas bubbles stay inside a pump chamber, a pump includes a primary pump chamber whose volume can be varied by driving a diaphragm, an inlet passage to allow a working fluid to flow into the primary pump chamber, an outlet passage to allow the working fluid to flow out of the primary pump chamber, and check valves to open and close at least the inlet passage. A resultant inertance value of the inlet passage is set to be smaller than a resultant inertance value of the outlet passage. A bubble discharging device to discharge gas bubbles remained in the primary pump chamber is further provided. As a result, it is possible to provide a pump capable of discharging gas bubbles with the bubble discharging device and thus maintain a discharging ability, even when the gas bubbles stay in the primary pump chamber.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a pump to move a working fluid byvarying a volume of a pump chamber by a piston or a movable wall, suchas a diaphragm, and specifically to a small high-power pump.

2. Description of Related Art

In the related art, there are pumps having a construction in which checkvalves are provided between an inlet passage and a pump chamber having avariable volume and between an outlet passage and the pump chamber,respectively. Further, in a case of a pump having a purpose oftransferring liquid, there is a related art structure that a thin wallportion is provided at an upstream side or downstream side passage of apump chamber and thus pulsation due to the liquid intermittently drivenis reduced through deformation of the passage (see, Japanese UnexaminedPatent Application Publication No. 2000-265963.

Furthermore, there is a related art high-power pump with highreliability, which was suggested by the present inventor, etc., capableof coping with high load pressure and high frequency driving byemploying a passage structure having a large inertance value in place ofa valve in an outlet passage and thus by using a force of fluid inertia.In a pump having such a structure, for the purpose of preventing asuction efficiency of the pump from being decreased due to pulsation inan inlet passage, a deformable structure is used in the inlet passage(see, Japanese Unexamined Patent Application Publication No.2002-322986.

Furthermore, there is a related art volume pump including a diaphragm tobe driven with a piezoelectric element, such as a PZT, a pump chamberwhose volume can be varied by the diaphragm, a hole to allow a fluid toflow into the pump chamber, and a hole to allow the fluid to flow out ofthe pump chamber, check valves being provided in the respective holes(see, for example, Japanese Unexamined Patent Application PublicationNo. 61-171891.

SUMMARY OF THE INVENTION

However, in the construction of Japanese Unexamined Patent ApplicationPublication No. 2000-265963 there is a problem that it is not possibleto cope with the high load pressure or high frequency driving, becausethe inlet passage and the outlet passage all require the check valveserving as a fluid resistance element. Thus, the pressure loss of thefluid is large through the two check valves. In a case where gas bubblesstay in the pump chamber, there is a problem that it is not possible toobtain a predetermined amount of discharge, because the pressure of theliquid in the pump chamber is not raised enough in the course ofreducing the volume of the pump chamber.

Furthermore, in the pumps having the constructions of JapaneseUnexamined Patent Application Publication No. 2002-322986 and JapaneseUnexamined Patent Application Publication No. 61-171891, since thevariation in volume of the pump chamber due to the deformation of thediaphragms is small, the pressure of the liquid in the pump chamber isnot raised enough in the course of reducing the volume of the pumpchamber when gas bubbles stay in the pump chamber. As a result, the flowcharacteristics of the pump are largely deteriorated. If things come tothe worst, it may be impossible to discharge the liquid.

The present invention provides a pump capable of discharging gas bubblesand thus maintaining a discharging ability, even when the gas bubblesstay inside a pump chamber.

A pump according to an aspect of the present invention includes a pumpchamber whose volume can be varied by driving a piston or a movablewall, an inlet passage to allow a working fluid to flow into the pumpchamber, an outlet passage to allow the working fluid to flow out of thepump chamber, and a fluid resistance element to open and close at leastthe inlet passage. A resultant inertance value of the inlet passage isset to be smaller than a resultant inertance value of the outletpassage. A bubble discharging device to discharge gas bubbles remainingin the pump chamber is further provided.

Here, a diaphragm, which is driven with an actuator, such as apiezoelectric element, may be used as the movable wall. Further, a checkvalve may be used as the fluid resistance element.

Furthermore, as the bubble discharging device, details of which will bedescribed later, for example, a secondary pump chamber, a pressurizingmechanism, a heating section, etc., which is used to apply a pressure tothe pump chamber, may be used.

According to this construction, since the pump includes the bubbledischarging device, the pump can be started even when gas bubbles stayin the pump chamber. Specifically, even when the working fluid is notfilled in the pump chamber. Further, when the gas bubbles stay in thepump chamber, although it is considered that the pressure in the pumpchamber is not sufficiently raised, the staying gas bubbles can bedischarged in driving the pump, due to the aforementioned bubbledischarging device. So it is possible to maintain performance of thepump, specifically, the discharge amount of the working fluid.

Further, in the aforementioned construction, the pump chamber mayinclude a primary pump chamber which communicates with the outletpassage and whose volume can be varied by driving a piston or a movablewall, and a secondary pump chamber which communicates with the inletpassage and functions as the bubble discharging device and whose volumecan be varied by driving a movable wall.

According to this construction, since the secondary pump chamber as thebubble discharging device is provided at the inlet passage side, theworking fluid of the inlet passage can be transferred to the primarypump chamber by driving the secondary pump chamber. Thus the pressure inthe primary pump chamber can be raised, so that it is possible todischarge the gas bubbles in the primary pump chamber.

The pump having the above construction may include a primary pumpchamber inlet passage to allow the working fluid to flow into theprimary pump chamber; a primary pump chamber outlet passage to allow theworking fluid to flow out of the primary pump chamber; a secondary pumpchamber inlet passage to allow the working fluid to flow into thesecondary pump chamber; and a secondary pump chamber outlet passage toallow the working fluid to flow out of the secondary pump chamber, andthe primary pump chamber inlet passage be the secondary pump chamberoutlet passage.

According to this construction, since the primary pump chamber inletpassage is also used as the secondary pump chamber outlet passage, theflow passage of the working fluid is shortened. Thus the size of thepump can be decreased, so that it is possible to reduce the fluidresistance of the flow passage.

The pump according to an aspect of the present invention may include afluid resistance element to open and close the primary pump chamberinlet passage; a fluid resistance element to open and close thesecondary pump chamber inlet passage; and a fluid resistance element toopen and close the secondary pump chamber outlet passage, and the fluidresistance element to open and close the primary pump chamber inletpassage may be the fluid resistance element to open and close thesecondary pump chamber outlet passage.

According to this construction, for example, when the movable wall ofthe secondary pump chamber is driven, a check valve, as the fluidresistance element of the secondary pump chamber inlet passage, isclosed. Then the working fluid, of which the pressure has been raised inthe secondary pump chamber, flows into the primary pump chamber.Further, when the working fluid is discharged from the primary pumpchamber, a check valve as the fluid resistance element of the primarypump chamber inlet passage is closed. In this way, since the insidepressure of the primary pump chamber can be raised, the gas bubblesstaying in both pump chambers can be compressed and then discharged tothe outside of the pump chambers.

Furthermore, since the fluid resistance element to open and close theprimary pump chamber inlet passage is the fluid resistance element toopen and close the secondary pump chamber outlet passage, two checkvalves, as the fluid resistance elements, are enough for two pumpchambers. So it is possible to simplify the structure of the pump, toreduce the number of components, and thus to accomplish low cost.Furthermore, it is also possible to reduce the fluid resistance.

In the pump having the aforementioned construction, the movable wallprovided in the secondary pump chamber may be a diaphragm in which apiezoelectric element is attached to at least one surface thereof, andthe secondary pump chamber and the diaphragm constitute a unimorph pumpor a bimorph pump.

According to this construction, the secondary pump chamber can beconstructed using a piezoelectric element attached to the diaphragm usedin related art pulsation reducing device for a flow passage. Further,since the unimorph pump and the bimorph pump have a large amount ofdisplacement of the diaphragm even under a low pressure, they cancombine the functions of the secondary pump chamber as a pulsationabsorbing device and the aforementioned bubble discharging device.

The pump having the above construction may include a driving switchcontrol unit for switching the driving between the secondary pumpchamber and the primary pump chamber.

By the driving switch control unit, for example, when the driving of thepump is started, the inner gas bubbles can be discharged by firstdriving the secondary pump chamber and then driving the primary pumpchamber. Then the primary pump chamber is continuously driven or theprimary pump chamber and the secondary pump chamber can be alternatelydriven, so that it is possible to obtain a stable discharge amount ofworking fluid during the driving of the pump.

Furthermore, a driving electrode and a detecting electrode may be formedin the piezoelectric element.

According to this construction, the state of the secondary pump chambercan be detected. Specifically, variation in the inside pressure of thesecondary pump chamber can be detected as displacements of thepiezoelectric element. It is thus possible to control the primary pumpchamber and the secondary pump chamber correspondingly to the variationin pressure by using the above-mentioned driving switch control unit.

Furthermore, the pump according to an aspect of the present inventionmay include a pressure detecting section to detect an inside pressure ofthe primary pump chamber.

According to this construction, the state inside the primary pumpchamber can be detected. So it is possible to efficiently drive the pumpcorrespondingly to the state inside the primary pump chamber.

Further, by combining the state inside the primary pump chamber with thestate inside the secondary pump chamber detected through the detectingelectrode of the secondary pump chamber, it is possible to drive thepump more efficiently than a case of driving the pump correspondingly toboth states of both pump chambers.

The above-mentioned pump according to an aspect of the present inventionmay include a pressurizing mechanism serving as the bubble dischargingdevice to raise and maintain the pressure of the working fluid existingin the pump chamber.

According to this construction, when the inside pressure of the pumpchamber is reduced due to the gas bubbles staying in the pump chamberand thus the working fluid cannot be discharged, the pressure of theworking fluid in the pump chamber can be raised and maintained by thepressurizing mechanism. As a result, since the volume of the gas bubblesis decreased, it is possible to discharge the gas bubbles in the pumpchamber by compressing the volume of the pump chamber through drivingthe piston or the movable wall, such as a diaphragm.

In the above-mentioned construction, the pressurizing mechanism mayinclude a variable-volume chamber and a flow passage to allow thevariable-volume chamber and the outlet passage to communicate with eachother.

According to this construction, since the variable-volume chambercommunicates with the outlet passage by pressing the variable-volumechamber, the pressurizing mechanism can simply generate a high pressurein the pump chamber communicating with the outlet passage.

In the above-mentioned construction, the variable-volume chamber may beformed of an elastic member.

According to this construction, by forming the variable-volume chamberout of the elastic member, the pressure can be smoothly raised due tothe introduction of the working fluid into the variable-volume chamber.Damages on the components constituting the pump due to the pressure canbe reduced or prevented. Further, the variable-volume chamber alsofunctions to reduce the pressure pulsation in the outlet passage. As aresult, it is possible to reduce or prevent the variation in pumpability from occurring due to influence of an external pipe to beconnected to the outlet passage.

Furthermore, in the above-mentioned construction, the pressurizingmechanism may include a volume varying mechanism to apply a pressure tovary the volume of the variable-volume chamber.

Here, an actuator may be employed as the volume varying mechanism.

According to this construction, since the volume varying mechanism tovary the volume of the variable-volume chamber is provided, it ispossible to control the volume of the variable-volume chambercorrespondingly to the state of the pump chamber.

In an aspect of the present invention, the pressurizing mechanism mayinclude a passage switching section to switch between a first mode wherethe working fluid flowing out of the pump chamber is introduced into thevariable-volume chamber and a second mode where the working fluidflowing out of the pump chamber is isolated from the variable-volumechamber.

According to this construction, for example, when it is detected thatgas bubbles exist in the pump chamber, it is possible to surely pressthe working fluid in the pump chamber with the elastic force of theelastic member constituting the variable-volume chamber, by setting thefirst mode where the working fluid flowing out of the pump chamber isintroduced into the variable-volume chamber. When the gas bubbles do notexist in the pump chamber, the working fluid is controlled not to beintroduced into the variable-volume chamber but to be discharged out ofthe pump chamber, so that it is possible to efficiently drive the pump.

The pump having the above construction may include a pressure detectingsection to detect an inside pressure of the variable-volume chamber.

In this way, by providing the pressure detecting device to detect theinside pressure of the variable-volume chamber, it is possible tocontrol the inside pressure of the variable-volume chamber within aproper range of pressure.

In the aforementioned pump, the pressure detecting device may beprovided in the pump chamber.

As a result, by detecting the inside pressure of the pump chamber anddetermining whether the gas bubbles stay in the pump chamber, it ispossible to suitably control the driving of the pump chamber and thepressurizing mechanism.

In the above construction, the inside pressure of the variable-volumechamber, which is pressurized by the pressurizing mechanism, may rangefrom about one atmosphere to about five atmospheres in a gauge pressure.

According to this construction, it is possible to reduce the volume ofthe gas bubbles staying in the pump chamber as enough as possible todischarge without damaging the components constituting the pump by thepressure.

Furthermore, the pressurizing mechanism may include a variable-volumechamber, a flow passage communicating with the outlet passage, and anopening and closing member to open and close the flow passage. Thepressurizing mechanism may be detachable from the outlet passage. Thevariable-volume chamber and the outlet passage may be allowed tocommunicate with each other by fitting the pressurizing mechanism intothe outlet passage.

In this way, when the detachable pressurizing mechanism is fitted intothe outlet passage, the outlet passage and the pressurizing mechanismcommunicate with each other. Thus the pressure in the variable-volumechamber is raised, so that the gas bubbles in the pump chamber aredischarged. When the gas bubbles do not stay in the pump chamber, it ispossible to realize a small and light pump in a state where thepressurizing mechanism is detached.

Furthermore, the pump according to an aspect of the present inventionmay include a heating section serving as the bubble discharging deviceprovided in the pump chamber.

According to this construction, the gas bubbles are moved from thestagnation points in the pump chamber by heating the staying gas bubbleswith the heating section provided in the pump chamber and thusincreasing the volume of the staying gas bubbles, so that it is possibleto easily discharge the gas bubbles.

The heating section may be received inside the wall of the pump chamber,or be arranged in a comer portion of the pump chamber.

In the pump chamber, the gas bubbles tend to stay at the comer portionsof the pump chamber or at the protruded wall portions of the pumpchamber. Accordingly, by receiving the heating section inside the wallof the pump chamber without generating any protruded portion, or byarranging the heating section at least at the comer portion of the pumpchamber, it is possible to make the gas bubbles not stay or to dischargethe staying gas bubbles from the corner portions of the pump chamberwhere the gas bubbles tend to stay.

Furthermore, a plurality of the heating sections may be provided.

In this way, by arranging the plurality of heating devices, it ispossible to reduce the amount of energy per unit time to be supplied tothe heating device. It is also possible to rapidly discharge the stayinggas bubbles while reducing or preventing destruction of the pump.

Furthermore, the above-mentioned pump may include a pressure detectingsection for detecting an inner pressure of the pump chamber.

As a result, by detecting the inside pressure of the pump chamber andchecking whether the gas bubbles stay in the pump chamber, it ispossible to suitably control the driving of the pump.

Furthermore, when the piston or the movable wall is being driven, aheating signal may be input to the heating section.

As a result, by heating the working fluid in the pump chamber with theheating section while allowing the piston or the diaphragm to operate,it is possible to raise the inside pressure of the pump chamber and thusto discharge the gas bubbles staying in the pump chamber.

In the above construction, a pulse-shaped heating signal may be input tothe heating section. The piston or the movable wall may be driven insynchronism with the heating signal.

Furthermore, since the aforementioned pump allows the heating section toheat the working fluid in a pulse shape and allows the diaphragm tooperate in synchronism with the pulse, it is possible to reduce theamount of energy consumed in the heating section, and to effectivelydischarge the gas bubbles staying in the pump chamber.

In the above pump, the heating section may heat the working fluid tochange the phase of the working fluid in contact with the heatingsection.

As a result, since the gas bubbles can be generated in the pump chamberdue to the change of phase and a complex and non-stagnated flow flowingout to the outlet passage can be caused in the pump chamber, it ispossible to easily discharge the gas bubbles staying in the pumpchamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional schematic illustrating a pumpaccording to a first exemplary embodiment of the present invention;

FIG. 2 is a graph illustrating inner states of the pump according to thefirst exemplary embodiment of the present invention;

FIG. 3 is a schematic illustrating a driving circuit of the pumpaccording to the first exemplary embodiment of the present invention;

FIG. 4 is a schematic illustrating a diaphragm for a secondary pumpchamber of a pump according to a second exemplary embodiment of thepresent invention;

FIG. 5 is a vertical cross-sectional schematic illustrating a part of apump according to a third exemplary embodiment of the present invention;

FIG. 6 is a schematic illustrating a driving circuit of the pumpaccording to the third exemplary embodiment of the present invention;

FIG. 7 is a vertical cross-sectional schematic illustrating a pumpaccording to a fourth exemplary embodiment of the present invention;

FIG. 8 is a schematic illustrating a driving circuit of the pumpaccording to the fourth exemplary embodiment of the present invention;

FIG. 9 is a vertical cross-sectional schematic illustrating a pumpaccording to a fifth exemplary embodiment of the present invention;

FIG. 10 is a vertical cross-sectional schematic illustrating apressurizing mechanism according to a sixth exemplary embodiment of thepresent invention;

FIG. 11 is a vertical cross-sectional schematic illustrating a part of apump according to the sixth exemplary embodiment of the presentinvention;

FIG. 12 is a vertical cross-sectional schematic illustrating a part of apump according to a seventh exemplary embodiment of the presentinvention;

FIG. 13 is a schematic illustrating a heater according to the seventhexemplary embodiment of the present invention;

FIG. 14 is a schematic illustrating a modified example of the heateraccording to the seventh exemplary embodiment of the present invention;

FIG. 15 is a schematic illustrating a driving circuit of the pump of theseventh exemplary embodiment of the present invention;

FIG. 16 is a schematic illustrating another modified example of theheater according to the seventh exemplary embodiment of the presentinvention; and

FIG. 17 is a vertical cross-sectional schematic illustrating a pumpaccording to another exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Now, exemplary embodiments of the present invention will be describedwith reference to the accompanying drawings.

The exemplary embodiments of the present invention are shown in FIGS. 1to 17.

First Exemplary Embodiment

FIGS. 1 to 3 show a pump 10 according to a first exemplary embodiment.

FIG. 1 is a vertical cross-sectional schematic illustrating a structureof the pump 10 according to the first exemplary embodiment of thepresent invention. In FIG. 1, the pump 10 includes a cup-shaped case 50to which a laminated piezoelectric element 70 is fixed, an inflowpassage 21 to introduce a working fluid, an outflow passage 28 todischarge the working fluid, and a pump case 20 having a secondary pumpchamber 24 and a primary pump chamber 27.

One end of the laminated piezoelectric element 70 is fixed to an insidebottom portion of the case 50 through a fixing device, such as adhesive.A primary pump chamber diaphragm 60 is closely fixed to both of a topsurface of an edge portion of the case 50 and a top surface of the otherend of the laminated piezoelectric element 70. The pump case 20 is fixedto the circumferential edge portion of the top surface of the primarypump chamber diaphragm 60 such that the airtightness of the fixedportions is maintained. The primary pump chamber 27 is formed in a spacebetween the primary pump chamber diaphragm 60 and a concave portionformed in a lower portion of the pump case 20.

A concave portion is provided in an upper portion of the pump case 20.The secondary pump chamber diaphragm 45 is airtightly fixed to a topsurface of an edge portion of the concave portion, thereby forming thesecondary pump chamber 24. The secondary pump chamber diaphragm 45 isformed out of a plate member thinner than the primary pump chamberdiaphragm 60, and is deformable with the inside pressure of thesecondary pump chamber 24. A plate-shaped piezoelectric element 71 isfixed to a top surface of the secondary pump chamber diaphragm 45. Thesecondary pump chamber diaphragm 45 and the plate-shaped piezoelectricelement 71 form a unimorph actuator.

The plate-shaped piezoelectric element 71 may be attached to bothsurfaces of the secondary pump chamber diaphragm 45 to form a bimorphactuator. In this case, the close attachment of the plate-shapedpiezoelectric element 71 in contact with the working fluid should benoted, while an actuator having a larger displacement can be formed.

Next, a construction along the flow passage of the working fluid will bedescribed. The inflow passage 21 is formed in an inlet connection tube30 protruded from the pump case 20, and communicates with the secondarypump chamber 24 through an inlet valve hole 22 for the secondary pumpchamber and an inlet valve fitting hole 23 for the secondary pumpchamber. An inlet check valve 41 for the secondary pump chamber as afluid resistance element to open and close the inlet valve hole 22 forthe secondary pump chamber is fixed to the edge of the inlet valvefitting hole 23 for the secondary pump chamber. An inlet valve hole 25for the primary pump chamber and an inlet valve fitting hole 26 for theprimary pump chamber are provided between the secondary pump chamber 24and the primary pump chamber 27. An inlet check valve 42 for the primarypump chamber as a fluid resistance element, including an opening andclosing member which can open and close the inlet valve hole 25 for theprimary pump chamber, is fixed to the edge of the inlet valve fittinghole 26 for the primary pump chamber.

The primary pump chamber 27 communicates with the outflow passage 28.The outflow passage 28 has a narrow tube portion connected to theprimary pump chamber 27 and a wide tube portion of which a sectionalarea is enlarged from an intermediate portion of the narrow tubeportion, which are formed continuously. An outer circumferential portionof the outlet passage constitutes the outlet connection tube 31.

Further, although not shown, tubes made of silicon rubber havingelasticity are connected to the inlet connection tube 30 and the outletconnection tube 31.

Next, an inertance value L of a flow passage is defined. Supposed that asectional area of the flow passage is S, a length of the flow passage isr, and a density of the working fluid is ρ, the following equation isobtained: L=ρ×r/S. Supposed that a pressure difference of the flowpassage is ΔP and a flow volume of the working fluid flowing in the flowpassage is Q. The following equation is obtained by deforming a dynamicequation of the fluid in the flow passage using the inertance value L:ΔP=L×dQ/dt.

The inertance value L indicates a degree of influence of a unit pressureon a variation of flow volume per unit time, where the variation of flowvolume per unit time becomes smaller with increase of the inertancevalue L and the variation of flow volume per unit time becomes largerwith decrease of the inertance value L.

The resultant inertance value, about a parallel connection of aplurality of flow passages or a serial connection of a plurality of flowpassages having different shapes may be calculated by composinginertance values of the respective flow passages similarly to theparallel connection or the serial connection of inductances in electriccircuits. For example, when two flow passages having inertance values ofL1 and L2, respectively, are connected in series, the resultantinertance value is given as L1+L2.

The inlet passage described hereinafter refers to a flow passageextending from the inside of the primary pump chamber 27 to an inlet endsurface of the inlet valve hole 25 for the primary pump chamber. In thefirst exemplary embodiment of the present invention, since the secondarypump chamber 24 having the secondary pump chamber diaphragm 45 as apulsation absorbing device is connected to an intermediate portion ofthe flow passage, the inlet passage refers to a flow passage extendingfrom the inside of the primary pump chamber 27 to a connection portionof the pulsation absorbing device.

Therefore, when the secondary pump chamber diaphragm 45 has a highrigidity and thus a small pulsation absorbing effect, it is necessary tocalculate the resultant inertance value of the primary pump chamberinlet passage up to the position of the pulsation absorbing device, suchas a tube at the upstream of the secondary pump chamber 24.

The outlet passage refers to a flow passage extending up to an outletend surface of the outflow passage 28, because the tube serving as thepulsation absorbing device is connected to the outlet connection tube31.

Next, the inertance value of an opening and closing member of the checkvalve is defined. The inertance value of the opening and closing memberis associated almost with a mass of the opening and closing member and asectional area of the flow passage (a valve hole) which is closed by theopening and closing member, and is given as (the inertance value of theopening and closing member)=((the mass of the opening and closingmember)/(the sectional area of the flow passage which is closed by theopening and closing member)²). For a time when the flow volume is small,by opening the flow passage from a state where the opening and closingmember closes the flow passage entirely, the inertance value of theopening and closing member indicates a degree of influence of a unitpressure on the variation of flow volume per unit time, similarly to theinertance value of the flow passage, where the variation of flow volumeper unit time becomes smaller with increase of the inertance value andthe variation of flow volume per unit time becomes larger with decreaseof the inertance value.

Next, an internal state of the pump, according to the first exemplaryembodiment when the pump operates, will be described with reference toFIG. 2. FIG. 1 will be also referred to.

FIG. 2 is a graph illustrating as waveforms relations of a drivingvoltage (V) of the laminated piezoelectric element 70 and a pressure(MPa) of the primary pump chamber 27 expressed in an absolute pressurewith respect to a time (ms), when the primary pump chamber 27 and thesecondary pump chamber 24 are filled with the working fluid which is aliquid (water) in the pump 10 according to the first exemplaryembodiment of the present invention. In FIG. 2, since the laminatedpiezoelectric element 70 is expanded with increase of the drivingvoltage, the primary pump chamber diaphragm 60 is raised, therebycompressing the volume of the primary pump chamber 27. In FIG. 2, it canbe seen that the pressure starts its increase due to the compression ofthe primary pump chamber 27 after passing through a trough of thedriving voltage. The inside pressure of the primary pump chamber 27 israpidly decreased after passing through a point of the driving voltagehaving an largest upward slope, and is dropped substantially down to anabsolute pressure of 0.

Specifically, first, when the primary pump chamber 27 is compressed in astate where the inlet check valve 42 for the primary pump chamber isclosed, the inside pressure of the primary pump chamber 27 is largelyincreased due to the large inertance of the outflow passage (outletpassage) 28. With the increase of the inside pressure of the primarypump chamber 27, the working fluid in the small tube portion isaccelerated. Thus the kinetic energy generating an inertia effect isaccumulated. When the slope of the expansion and contraction speed ofthe laminated piezoelectric element 70 is decreased, the working fluidtends to continuously flow due to the inertia effect from the kineticenergy of the working fluid in the outlet passage accumulated in themeantime, so that the inside pressure of the primary pump chamber 27 israpidly dropped, and thus becomes smaller than the inside pressure ofthe secondary pump chamber 24.

At this time point, the inlet check valve 42 for the primary pumpchamber is opened due to the pressure difference, so that the workingfluid flows in the primary pump chamber 27 from the secondary pumpchamber 24. At that time, since the sum of the resultant inertance valueof the inlet passage of the primary pump chamber 27 and the inertancevalue of the inlet check valve 42 for the primary pump chamber servingas the opening and closing member is smaller enough than the inertancevalue of the outlet passage described above, the efficient inflow of theworking fluid is caused.

This state where the outflow and inflow to the primary pump chamber 27occur simultaneously is continued until the laminated piezoelectricelement 70 is compressed and then is expanded again. This denotes theflat portion of the inside pressure of the primary pump chamber 27 inFIG. 2.

Specifically, in the pump 10 according to the first exemplary embodimentof the present invention, since the discharge and suction are continuedfor a long time, it is possible to allow a large flow volume to flow.Since the inside of the pump chamber has a very high pressure, it ispossible to cope with a high load pressure.

At that time, in the secondary pump chamber 24, the secondary pumpchamber diaphragm 45 absorbs the pulsation through deformation by theinside pressure of the secondary pump chamber 24. As a result, theinflow of the working fluid from the inflow passage 21 having a largeinertance value to the secondary pump chamber 24 is a static flow havinga small pulsation, and the inlet check valve 41 for the secondary pumpchamber is continuously opened. In this way, the secondary pump chamberdiaphragm 45 has an effect of suppressing the pulsation of the inflowpassage 21 while keeping the inertance value of the inlet passage of theprimary pump chamber 27 small through its deformation. At that time,since the opened state of the inlet check valve 41 for the secondarypump chamber is continued, a problem such as generation of fluidresistance or fatigue failure does not occur.

Next, a priming action when the pump 10 starts its operation will bedescribed with reference to FIGS. 1 and 3.

FIG. 3 is a schematic of a driving circuit system according to the firstexemplary embodiment of the present invention. A priming action is anaction that in a case where gas bubbles stay in the pump, a liquid isfilled using another pump when the primary pump chamber 27, not havingan ability of voluntarily absorbing the liquid, is started. In FIG. 3,the driving circuit system of the pump 10 includes the laminatedpiezoelectric element 70 to drive the primary pump chamber diaphragm 60,the plate-shaped piezoelectric element 71 to drive the secondary pumpchamber diaphragm 45, a switching circuit 85 serving as a driving switchcontrol unit to switch the driving between the laminated piezoelectricelement 70 and the plate-shaped piezoelectric element 71, and a pumpdriving control circuit 80 to control the driving of the pump 10.

In a case where the working fluid is not filled in the primary pumpchamber 27, a driving voltage generated by the pump driving controlcircuit 80 is applied to the plate-shaped piezoelectric element 71attached to the secondary pump chamber diaphragm 45 by he switchingcircuit 85 at an initial stage of the pump operation. The drivingvoltage has, for example, a sine waveform. Since the secondary pumpchamber 45 is formed out of a thin plate member and constitutes aunimorph actuator having a large amount of displacement, the second pumpchamber 24 causes large variation in volume with the driving voltage.The inlet check valve 41 for the secondary pump chamber is arranged atthe inlet side of the secondary pump chamber 24, and the inlet checkvalve 42 for the primary pump chamber is arranged at the outlet sidethereof. The inlet check valve 42 for the primary pump chamber functionsas the outlet check valve of the secondary pump chamber 24.

As a result, since the secondary pump chamber 24 includes the checkvalves at both of the inlet and outlet and thus has a large amount ofvariation in volume, the secondary pump chamber functions as a pumpcapable of transferring both gas and liquid. Since the secondary pumpchamber 24 and the primary pump chamber 27 discharge the gas and thusare filled with the liquid which is the working fluid, the pump canoperate through variation in volume of the primary pump chamber 27. Theswitching circuit 85 is switched to apply the driving voltage to thelaminated piezoelectric element 70 after sufficient time passes througha timer (not shown), thereby automatically enabling high-poweroperation.

Furthermore, during operation of the primary pump chamber 27, it ispossible to detect the operating condition of the secondary pump chamberdiaphragm 45 by detecting a terminal voltage of the plate-shapedpiezoelectric element 71. In a case where gas bubbles in the workingfluid stay in the primary pump chamber 27 to deteriorate the pumpability, the amount of operation of the secondary pump chamber diaphragm45 is decreased. At that time, by allowing the secondary pump chamberdiaphragm 45 to operate by the plate-shaped piezoelectric element 71,thus discharging the gas bubbles, and then switching the driving voltagesuch that the primary pump chamber diaphragm 60 is driven by thelaminated piezoelectric element 70, the pump ability can be recovered.The priming action is executed by performing the aforementioned drivingcontrol.

Therefore, in the aforementioned first exemplary embodiment, since thesecondary pump chamber 24 includes the check valves 41, 42 at both ofthe inlet and outlet and thus has a large amount of variation in volume,the secondary pump chamber functions as a pump capable of transferringboth of the gas and the liquid. Since the secondary pump chamber 24 andthe primary pump chamber 27 discharge the gas and thus are filled withthe liquid which is the working fluid, the pump can operate throughvariation in volume of the primary pump chamber 27.

The switching circuit 85 is switched to apply the driving voltage to thelaminated piezoelectric element 70 of the primary pump chamber 27 aftersufficient time passes through the timer, thereby automatically enablingthe high-power operation.

Furthermore, during operation of the primary pump chamber 27, it ispossible to detect the operating condition of the secondary pump chamberdiaphragm 45 by detecting the terminal voltage of the plate-shapedpiezoelectric element 71. In a case where gas bubbles in the workingfluid stay in the primary pump chamber 27 to deteriorate the pumpability, the amount of operation of the secondary pump chamber diaphragm45 is decreased. At that time, by allowing the secondary pump chamberdiaphragm 45 to operate by he plate-shaped piezoelectric element 71,thus discharging the gas bubbles, and then switching the driving voltagesuch that the primary pump chamber diaphragm 60 is driven by thelaminated piezoelectric element 70, the pump ability can be recovered.

Furthermore, since the primary pump chamber inlet passage is thesecondary pump chamber outlet passage and the fluid resistance element(the check valve 42) to open and close the primary pump chamber inletpassage is the fluid resistance element to open and close the secondarypump chamber outlet passage, the flow passage of the working fluid isshortened, so that it is possible to reduce the fluid resistance of theflow passage. As a result, it is possible to simplify the structure ofthe pump 10 and to reduce the number of components, thereby realizinglow cost.

In the first exemplary embodiment described above, a case where thediaphragm 60 is used to cause the variation in volume of the primarypump chamber 27 has been described, but this may be also accomplished byusing a piston.

Second Exemplary Embodiment

Next, a second exemplary embodiment of the present invention will bedescribed with reference to FIG. 4.

The pump according to the second exemplary embodiment has a basicstructure similar to the aforementioned first exemplary embodiment, butis different from the first exemplary embodiment in that a part of adriving electrode 52 attached to the plate-shaped piezoelectric element71 of the secondary pump chamber 24 is separated and forms a detectingelectrode 53.

FIG. 4 is a schematic of the pump according to the second exemplaryembodiment as seen from the secondary pump chamber diaphragm side. InFIG. 4, a part of the electrode 52 formed on the plate-shapedpiezoelectric element 71 attached to the top surface of the secondarypump chamber diaphragm 45 is separated to form the detecting electrode53.

Next, a function of the detecting electrode will be described. Duringthe priming action, such as the time of starting the pump, the drivingvoltage is applied to the plate-shaped piezoelectric element 71 in theaforementioned first exemplary embodiment. However, in the secondexemplary embodiment, since the detecting electrode 53 is isolated, itis possible to detect movement of the secondary pump chamber diaphragm45 even during the priming action (when the driving voltage is appliedto the plate-shaped piezoelectric element 71). When the gas in thesecondary pump chamber 24 is discharged through the operation of thesecondary pump chamber diaphragm 45 and thus the liquid is filled in thesecondary pump chamber 24, the movement of the secondary pump chamberdiaphragm 45 is decreased due to difference in compression rate thereof,and shortly thereafter the primary pump chamber 27 is thus filled withthe working fluid. Therefore, when a long tube is connected to theinflow side, timing when the priming action is completed can be detectedmore accurately than a case where time management is performed, so thatit is possible to switch the driving voltage toward the laminatedpiezoelectric element 70 attached to the primary pump chamber diaphragm60 for a short time.

Furthermore, by independently connecting the driving circuits to therespective piezoelectric elements of the primary pump chamber diaphragm60 and the second pump chamber diaphragm 45, and always monitoring thedetecting electrode 53, it is possible to correctly perform the primingaction without switching the circuits even in a case of operationfailure due to interfusion of gas bubbles, etc. during operation of thepump.

Therefore, according to the second exemplary embodiment described above,since the detecting electrode 53 is isolated, it is possible to detectthe movement of the secondary pump chamber diaphragm 45 during thepriming action, and to accurately detect the timing when the primingaction is completed, so that it is possible to switch the drivingvoltage toward the laminated piezoelectric element 70 of the primarypump chamber diaphragm 60 for a short time.

Furthermore, by independently connecting the driving circuits to therespective piezoelectric elements of the primary pump chamber diaphragm60 and the second pump chamber diaphragm 45, and always monitoring thedetecting electrode, it is possible to correctly perform the primingaction without switching the circuits even in a case of operationfailure due to interfusion of gas bubbles, etc. during operation of thepump.

Third Exemplary Embodiment

Next, a third exemplary embodiment of the present invention will bedescribed with reference to FIGS. 5 and 6. The pump according to thethird exemplary embodiment has a basic structure similar to theaforementioned first exemplary embodiment, but is different from thefirst exemplary embodiment in that the pump includes a pressure sensor90 in the primary pump chamber 27. Descriptions of constituent elementscommon to the first exemplary embodiment will be omitted.

FIG. 5 is a vertical cross-sectional schematic of the pump according tothe third exemplary embodiment of the present invention, and FIG. 6 is aschematic of the driving circuit of the pump according to the thirdexemplary embodiment. In FIG. 5, two-stepped concave portion 35 isformed in an inside top wall of the primary pump chamber 27. Thepressure sensor 90 made of the same material as the aforementionedplate-shaped piezoelectric element 71 is fixed to the step of theconcave portion 35 toward the primary pump chamber 27. An electrode, notshown, is formed on the surface of the pressure sensor 90. The pressuresensor is connected to the pump driving control circuit 80 (see FIG. 6)to be described later. The concave portion 35 has a gap so that thepressure sensor 90 does not come in contact with the wall when it isbent.

In FIG. 6, the driving circuit system of the pump 10 includes thelaminated piezoelectric element 70 to drive the primary pump chamberdiaphragm 60, the plate-shaped piezoelectric element 71 to drive thesecondary pump chamber diaphragm 45, the pressure sensor 90 to detectthe inside pressure of the primary pump chamber 27, and the pump drivingcontrol circuit 80 to control the driving of the pump 10.

In FIGS. 5 and 6, when gas bubbles stay in the primary pump chamber 27,the inside pressure of the primary pump chamber 27 is decreased. Thisstate is detected by the pressure sensor 90. A driving signal is outputto the plate-shaped piezoelectric element 71 from the pump drivingcontrol circuit 80, so that the secondary pump chamber diaphragm 45 isdriven to increase the inside pressure of the secondary pump chamber 24.Accordingly, the gas bubbles staying in the primary pump chamber 27 aredischarged from the pump chamber. Specifically, the plate-shapedpiezoelectric element 71 of the secondary pump chamber diaphragm 45 isdriven in synchronism with variation of the inside pressure of theprimary pump chamber 27.

In the first to third exemplary embodiments, the pump not including acheck valve at the outflow passage 28 side of the primary pump chamber27 has been constructed. But in the pump including the check valve andrequiring the priming action, the similar advantages can be obtained.

Therefore, according to the third exemplary embodiment, since thepressure sensor 90 is provided in the primary pump chamber 27, it ispossible to accurately detect the operation failure due to interfusionof the gas bubbles into the primary pump chamber 27. Furthermore, in thethird exemplary embodiment of the present invention, since theplate-shaped piezoelectric element 71 of the secondary pump chamberdiaphragm 45 can be driven in synchronism with the primary pump chamberdiaphragm 60, it is possible to further enhance the suction efficiencyof the primary pump chamber 27, so that it is possible provide ahigher-power pump.

Fourth Exemplary Embodiment

Next, a pump according to a fourth exemplary embodiment of the presentinvention will be described with reference to FIGS. 7 and 8. The fourthexemplary embodiment basically has the technical spirit of the firstexemplary embodiment, but is different from the first exemplaryembodiment in that a pressurizing mechanism 150 is provided as a bubbleexclusion unit in place of the secondary pump chamber 24 (see FIG. 1).

FIG. 7 is a vertical cross-sectional schematic of the pump according tothe fourth exemplary embodiment of the present invention. In FIG. 7, thepump 100 basically includes the cup-shaped case 50 to which thelaminated piezoelectric element 70 is fixed, an inflow passage 121 tointroduce the working fluid, an outflow passage 128 to discharge theworking fluid, a pump case 120 having a pump chamber 127, and apressurizing mechanism 150 (surrounded with a broken line in the figure)to apply pressure to the pump chamber 127.

In the cup-shaped case 50, one end of the laminated piezoelectricelement 70 is fixed to an inside bottom portion thereof. The diaphragm60 is fixed to the edge portion of the case 50 and a top surface of theother end of the laminated piezoelectric element 70. A pump case 120 isairtightly fixed to the top surface of the diaphragm 60. The pumpchamber 127 is formed in a space between the diaphragm 60 and the bottomof the pump case 120.

The inflow passage 121 and the outflow passage 128 are formed toward thepump chamber 127. In the inflow passage 121, a check valve 122 as afluid resistance element to open and close the inflow passage 121 isprovided at a connection portion with the pump chamber 127. A part ofthe outer circumference of a cylindrical portion constituting the inflowpassage 121 functions as an inlet connection tube 130 to be connected toan external tube, not shown. The outflow passage 128 includes a narrowtube portion connected to the pump chamber 127 and a wide tube portionof which a sectional area is enlarged in the way, which are formedcontinuously. The outer circumference of a cylindrical portionconstituting the outflow passage 128 functions as an outlet connectiontube 131 to be connected to an external tube, not shown. Here, forexample, tubes made of silicon rubber can be used as the external tubes.

The pressure sensor 90 as the pressure detecting section to detect theinside pressure of the pump chamber 127 is fixed to the inside top wallof the pump chamber 127.

The pump 100 is provided with the pressurizing mechanism 150 surroundedwith a broken line in the figure.

The pressurizing mechanism 150 includes a metallic bellows 151, which isan elastic member, an actuator 170 formed out of a piezoelectric elementas a volume varying mechanism of the bellows 151, and an shutoff valve140 to shut off the movement of the working fluid in the outflow passage128. The bellows 151 is closely fixed to a side surface of the outletconnection tube 131. Its opening portion 152 is connected to the flowpassage 132 communicating with the outflow passage 128.

A variable-volume chamber is formed inside the bellows 151. A pressuresensor 91, as the pressure detecting section to detect the insidepressure of the bellows 151, is provided inside the bellows. The volumeof the bellows 151 is varied by the actuator 170.

In the fourth exemplary embodiment, an end of the actuator 170 oppositeto the bellows 151 is fixed to the side of the inlet connection tube130. The actuator is reciprocated by a driving section, not shown. Theactuator includes a pressing section 171 to compress the bellows 151.The pressing section is driven by the pump driving control circuit 180(see FIG. 8).

The sectional area of the wide tube portion of the outflow passage 128at a position connected to the bellows 151 is double the sectional areaof the narrow tube portion. For this reason, the flow rate of the fluidpassing through the flow passage 132 connected to the bellows 151 isdecreased, so that the energy loss of the fluid during passing the flowpassage can be reduced.

The inertance value relation important in driving the pump according toan aspect of the present invention has been described in the firstexemplary embodiment, and thus its description is omitted. The inletpassage and the outlet passage in the fourth exemplary embodiment willbe defined.

In the flow passage to allow the working fluid to flow into the pumpchamber 127, the flow passage extending from the opening portion of thepump chamber 127 to the connection with a pulsation absorbing device isdefined as the inlet passage. Here, the pulsation absorbing devicesufficiently reduces the variation in the inside pressure of the flowpassage. In addition, a flow passage made of material, such as siliconrubber, resin, thin metal, which can be easily deformed with the insidepressure, an accumulator connected to the flow passage, a compositionflow passage to compose pressure variations having a plurality ofdifferent phases, etc. correspond to the pulsation absorbing device.

In the fourth exemplary embodiment, since the external tube, such as asilicon rubber tube, is connected to the inlet connection tube 130, theflow passage extending from the opening portion of the pump chamber 127to the end surface of the connection side of the silicon rubber tube inthe inflow passage 121, that is, the inflow passage 121 itself, isdefined as the inlet passage.

The outlet passage is defined similarly to the inlet passage. In theflow passage to which the working fluid is discharged from the pumpchamber 127, a flow passage extending from the opening portion of thepump chamber 127 to a connection portions with the pulsation absorbingdevice is defined as the outlet passage. In the fourth exemplaryembodiment according to the present invention, since the bellows 151 inthe way of the outflow passage 128 has a function of absorbing thepressure pulsation in a discharge mode to be described later, theoutflow passage 128 extending from the opening portion of the pumpchamber 127 to the connection portion with the bellows 151 is defined asthe outlet passage.

Next, a case where the pump 100 according to the fourth exemplaryembodiment is driven in the discharge mode will be described.

The discharge mode refers to an operation mode in which the workingfluid is allowed to flow out toward the downstream of the outflowpassage 128, and is performed in a case where the working fluid isfilled in the pump chamber 127 and thus gas bubbles do not stay therein.At that time, the shutoff valve 140 does not shut off the outflowpassage 128. The pressing section 171 of the actuator 170 is separatedfrom the bellows 151, as shown in FIG. 7. As a result, the bellows 151can be freely deformed elastically with the inside pressure. The bellows151 functions to reduce the pressure pulsation in the outflow passage128. Accordingly, even if an external tube, made of any material, isconnected to the outlet connection tube 131, the inertance value of theoutlet passage is not influenced, so that it is possible to reduce orprevent change in the pump ability due to the external tube. Only if avariable-volume chamber is formed of an elastic member in place of thebellows 151, can the same advantage be obtained.

Next, the internal state of the pump 100 according to the fourthexemplary embodiment when it is driven will be described. The internalstate of the pump 100 is similar to the above first exemplary embodiment(see FIG. 2), the description thereof is omitted. Thus features of thefourth exemplary embodiment will be described in detail.

The features are described with reference to FIGS. 2 and 7. In FIG. 2,as can be seen from the fact that the inside pressure of the pumpchamber 127 is raised up to about 2 MPa, the pump 100 according to thefourth exemplary embodiment causes a high pressure in the pump chamber127, thereby obtaining a high power. For this reason, specifically whengas bubbles stay in the pump chamber 127, the variation in volume(hereinafter, referred to as exclusion volume) of the pump chamber 127generated due to the deformation of the diaphragm 60 is used to compressthe gas bubbles during the time when the laminated piezoelectric element70 turns to the state where it is most expanded from the state where itis most contracted, and thus does not contribute to increase the insidepressure of the pump chamber 127, so that the pump cannot operateproperly. For this reason, it is important to exclude the staying gasbubbles rapidly.

Subsequently, a case where the pump 100 according to the fourthexemplary embodiment is driven in a bubble discharge mode will bedescribed with reference to FIGS. 7 and 8.

FIG. 8 is a schematic of the driving circuit of the pump 100 accordingto the fourth exemplary embodiment. Here, the bubble discharge moderefers to an operation mode to be performed when the gas bubbles stay inthe pump chamber 127. In FIG. 8, the driving circuit system of the pump100 includes the pressure sensor 90 (see FIG. 7) to detect the insidepressure of the pump chamber 127, the pressure sensor 91 to detect theinside pressure of the bellows 151, the pressurizing mechanism 150, anda pump driving control circuit 180 to control them.

Next, the discharge of gas bubbles existing by means of the pressurizingmechanism 150 when the pump is driven in the bubble discharge mode willbe described.

When the maximum inside pressure of the pump chamber detected by thepressure sensor 90 is smaller than, specifically a half or less of, themaximum inside pressure of the pump chamber in the normal driving underthe driving condition, the pump driving control circuit 180 determinesthat gas bubbles stay in the pump chamber 127. Then, the pump drivingcontrol circuit 180 gives an instruction to the pressurizing mechanism150. In response to the instruction, first, the shutoff valve 140 isswitched not to shut off the outflow passage 128. Next, the actuator 170in FIG. 7 allows the pressing section 171 to extend left and to come incontact with the bellows 151, and then compresses the bellows 151 in theleft direction, so that the volume of the chamber formed out of thebellows 151 is largely reduced. As a result, the gas bubbles staying inthe chamber formed out of the bellows 151 can be allowed to flow out tothe downstream from the shutoff valve 140.

Next, the shutoff valve 140 shuts off the outflow passage 128, and theactuator 170 allows the pressing section 171 to be contracted andseparated from the bellows 151. Since the bellows 151 is formed of anelastic member, it is recovered to the original state with its ownelastic force. In this way, the working fluid is filled in the bellows151. Subsequently, the actuator 170 is allowed to compress the bellows151 again. As a result, the pressure of the working fluid existing fromthe inside of the bellows 151 to the pump chamber 127 can be raised.

The volume of the gas bubbles staying in the pump chamber 127 isdecreased through the pressing, and the volume of the gas bubbles can bemade to be smaller enough than the exclusion volume. At that time, it isnecessary to set the chamber of the bellows 151 to about one atmosphereor more in a gauge pressure, preferably a pressure between about oneatmosphere and five atmospheres. By allowing the pump driving controlcircuit 180 to control the actuator 170 to compress the bellows 151 onthe basis of the detected value by the pressure sensor 91 to detect thepressure of the chamber formed out of the bellows 151, it is possible toraise the inside pressure of the bellows 151 up to a proper pressure.

Subsequently, when the laminated piezoelectric element 70 is driven,like in the discharge mode, the inside pressure of the pump chamber 127is raised enough and the working fluid is discharged from the pumpchamber 127 to the outflow passage 128. The gas bubbles staying in thepump chamber 127 flows in the bellows 151 with the flow of the workingfluid in the pump chamber 127.

The pump driving control circuit 180 includes a timer (not shown) tocount the time when the laminated piezoelectric element 70 is drivenafter the shutoff valve 140 shuts off the outflow passage 128. After apredetermined time interval, as a time interval enough to discharge thegas bubbles staying in the pump chamber 127, is counted with the timer,the shutoff valve 140 releases the shutoff of the outflow passage 128and the actuator 170 is contracted up to the position where it isseparated from the bellows 151. Thereafter, the bubble discharge mode isfinished.

At that time, the inside pressure of the bellows 151 is raised due tothe working fluid discharged from the pump chamber 127. But the bellowsis designed such that the deformation due to the pressure is suppressedwithin an allowable range of elastic deformation. In this way, byforming the variable-volume chamber out of an elastic member, thepressure can be made to be smoothly raised due to the introduction ofthe working fluid, so that it is possible to prevent destruction of theconstituent elements of the pump 100.

In addition, the pump driving control circuit 180 may be allowed tocontrol the actuator 170 by using values detected by the pressure sensor91 provided in the bellows 151, so that it may be possible to suppressthe inside pressure of the bellows 151 from being raised.

The pump may be constructed so that a relief valve is provided in thebellows 151, and it is possible to surely suppress the inside pressureof the bellows 151 from being raised by opening the relief valve whenthe inside pressure of the bellows 151 is too high.

Therefore, in the fourth exemplary embodiment, since the pressurizingmechanism 150 to raise and maintain the pressure of the working fluidexisting in the pump chamber 127 is provided, it is possible to raiseand maintain the pressure of the working fluid existing in the pumpchamber 127, when the gas bubbles stay in the pump chamber 127, theinside pressure of the pump chamber 127 is reduced. Thus it is notpossible to discharge the working fluid. As a result, the volume of thegas bubbles is decreased, so that it is possible to discharge the gasbubbles in the pump chamber by compressing the volume of the pumpchamber 127 through the operation of the diaphragm 60.

The pressurizing mechanism 150 presses the bellows 151. But since thevariable-volume chamber of the bellows 151 communicates with the outflowpassage 128, it is possible to simply generate a high pressure in thepump chamber 127 communicating with the outflow passage 128.

Furthermore, by forming the variable-volume chamber out of an elasticmember, the increase in pressure due to introduction of the workingfluid into the variable-volume chamber is smoothed, so that it ispossible to prevent the constituent elements of the pump from beingdamaged due to the pressure. Furthermore, by forming the variable-volumechamber out of an elastic member, the variable-volume chamber can beallowed to have a function of reducing the pressure pulsation in theoutlet passage. As a result, it is possible to reduce or prevent thepump ability from be varied due to influence of the external tubeconnected to the outlet passage.

First Modified Example of Fourth Embodiment

In a modified example of the fourth exemplary embodiment describedabove, the detected value of the pressure sensor 90 in the pump chamber127 may be checked, for example, by arbitrarily setting the timeinterval to be counted by the timer of the pump driving control circuit180 and allowing the pump to operate in the discharge mode after thebubble discharge mode is finished.

According to this modified example, by repeatedly performing theoperation of the bubble discharge mode until the gas bubbles aredischarged, it is possible to surely discharge the gas bubbles.

In the fourth exemplary embodiment described above, since the operationof the bubble discharge mode is executed when it is determined using thepressure sensor 90 in the pump chamber 127 that the gas bubbles stay,the operation of the bubble discharge mode is not executed wastefully.But the operation of the bubble discharge mode may be executed at propertime intervals.

In this case, the pressure sensor 90 can be omitted, so that it ispossible to simplify the structure.

Furthermore, when the inflow passage 121 and the outflow passage 128 areconnected to the external tubes, it is possible to raise and maintainthe inside pressure of the pump chamber 127 by pressing the bellows 151with the actuator 170 without the shutoff valve 140, thereby obtainingthe same advantage. Furthermore, although the actuator 170 is providedto press the bellows 151, the same advantage can be obtained, even whena display device through which a user can view an output of the pressuresensor 91 is provided and the user manipulates the shutoff valve 140 topress the bellows 151.

Second Modified Example of Fourth Embodiment

In the fourth exemplary embodiment, the pressure sensor 90 has beenprovided as the pressure detecting device for the pump chamber in thepump chamber 127, but a different device may be employed.

For example, the inside pressure of the pump chamber 127 may becalculated by measuring the deformation of the diaphragm 60 with astrain gauge or a displacement sensor.

Further, the inside pressure of the pump chamber 127 may be calculatedby measuring the deformation of the case 50 with a strain gauge.

Furthermore, the inside pressure of the pump chamber 127 may becalculated by measuring the deformation of the opening and closingmember in a state where the check valve 122 is closed, with a straingauge or a displacement sensor.

Furthermore, the inside pressure of the pump chamber 127 may becalculated by measuring current to drive the laminated piezoelectricelement 70 with a current sensor. Furthermore, by providing a straingauge in the laminated piezoelectric element 70, the inside pressure ofthe pump chamber 127 may be calculated on the basis of a voltage appliedto the laminated piezoelectric element 70 and the measured value by thestrain gauge. At that time, any type of strain gauge which detects thequantity of deformation by using variation in resistance, variation incapacitance, or variation in voltage may be used as the strain gauge. Asthe inside pressure detecting device of the bellows 151, a structure ofcalculating the pressure by detecting the deformation of the bellows 151with a strain gauge may used.

Third Modified Example of Fourth Embodiment

In the fourth exemplary embodiment described above, a piezoelectricelement has been employed as the actuator 170. But an electromagnetictype actuator, a shape-memory alloy type actuator, etc. in addition tothe piezoelectric element may be employed. Since the shape-memory alloytype actuator can realize a large quantity of deformation with a simplestructure, it is preferable.

Furthermore, the elastic member forming the variable-volume chamber maybe made of rubber or resin material. But the elastic member made ofmetal is specifically preferable because it can reduce or preventvaporization of the working fluid. Furthermore, the variable-volumechamber may have a film shape or a diaphragm shape. But since thebellows shape described in the fourth exemplary embodiment can cause alarge quantity of deformation and the laminated piezoelectric element 70can be driven in the bubble discharge mode continuously for a long time,it is preferable in that the gas bubbles can be easily discharged.

Therefore, according to the construction of the modified example of thefourth exemplary embodiment, it is possible to obtain the advantagesimilar to the fourth exemplary embodiment.

Fifth Exemplary Embodiment

Next, a pump according to a fifth exemplary embodiment of the presentinvention will be described with reference to FIG. 9.

The pump according to the fifth exemplary embodiment has the basicstructure similar to the fourth exemplary embodiment (see FIG. 7), butis different from the fourth exemplary embodiment in that the pump has astructure of switching between a first mode where the working fluidflowing out of the pump chamber 127 is introduced into the chamberformed out of the bellows 151 and a second mode where the chamber formedout of the bellows 151 is shut off from the flow of the working fluidflowing out of the pump chamber 127. Therefore, the difference will bepaid attention to. The same functional members are denoted by the samereference numerals as the fourth exemplary embodiment (see FIG. 7).

FIG. 9 shows a vertical cross-sectional schematic of the pump 100according to the fifth exemplary embodiment. In FIG. 9, the pressurizingmechanism 150 surrounded with a broken line is provided in the outflowpassage 128. The pressurizing mechanism 150 includes the metallicbellows 151 formed of an elastic member, and a switching valve 190(surrounded with two-dot chain line in the drawing) which is a passageswitching device. The switching valve 190 includes a switching valve 182to open and close the flow passage 132 communicating with the outflowpassage 128 at the opening portion 152 of the chamber formed out of thebellows 151, and a switching valve 183 to open and close the outflowpassage 128.

The switching valve 190 functions as switching a first connection statewhere, the outflow passage 128 extending from the pump chamber 127 tothe switching valve 182, and the outflow passage 128 at the downstreamside thereof, communicates with each other, by opening the switchingvalve 183, and the chamber formed out of the bellows 151 is shut offfrom the outflow passage 128 by closing the switching valve 182, and asecond connection state where, the outflow passage 128 extending fromthe pump chamber 127 to the switching valve 182 and the chamber formedout of the bellows 151 communicate with each other, and the outflowpassage 128 at the more downstream side than the switch valve 183, isshut off by closing the switching valve 183.

In the outflow passage 128, the sectional area of the outflow passage128 at the position at which the switching valve 183 is arranged isdouble the sectional area of the narrow flow passage portion of theoutflow passage 128 connected to the pump chamber 127. The reason hasbeen described in the fourth exemplary embodiment. The pressure sensor91 as an inside pressure detecting device of the bellows to detect thepressure of the chamber formed out of the bellows 151, is provided inthe bellows 151.

Here, definitions of the inlet passage and the outlet passage, andrelations of the inertance values in the fifth exemplary embodiment aresimilar to the fourth exemplary embodiment.

Next, a case where the pump 100 according to the fifth exemplaryembodiment is driven in the discharge mode will be described. In thefifth exemplary embodiment, in the discharge mode, the switching valve190 is switched into the first connection state to allow the workingfluid to flow out toward the downstream of the outflow passage 128. Atthat time, the pressure waveform in the pump chamber 127 when thelaminated piezoelectric element 70 is driven is similar to the firstexemplary embodiment (see FIG. 2). For this reason, similarly to thefirst exemplary embodiment, since the discharge and the absorptionsimultaneously occur, a large flow volume can be transferred. Since thepump chamber has a very high inside pressure, it is possible to copewith a high load pressure. When the gas bubbles stay in the pump chamber127, it has been already described in the first exemplary embodimentthat the pump does not operate properly.

Next, the bubble discharge mode, which is executed when the gas bubblesstay in the pump chamber, will be described. Further, although notshown, in the switching valve control system, if the pump drivingcontrol circuit determines that the gas bubbles stay in the pump chamber127, the pump driving control circuit gives an instruction to theswitching valve 190. Thus the switching valve 190 is switched into thesecond connection state from the first connection state.

At that time, since the inside of the bellows 151 is pressurized up toabout one atmosphere or more in a gauge pressure, preferably to apressure between about one atmosphere and five atmospheres, the pumpchamber 127 is almost pressurized up to the above pressure. In this way,by forming the variable-volume chamber out of an elastic member, it ispossible to apply the pressure only with the elastic force of theelastic member.

Since the volume of the gas bubbles staying in the pump chamber 127becomes smaller than the exclusion volume of the pump chamber 127through the pressing, the gas bubbles are discharged into the bellows151 through the driving of the laminated piezoelectric element 70, asdescribed in the fourth exemplary embodiment. Since the pump drivingcontrol circuit includes a timer (not shown) to count the time intervalwhen the laminated piezoelectric element 70 is driven after theswitching valve 190 is switched into the second connection state, apredetermined time interval is counted as the time interval enough todischarge the gas bubbles staying in the pump chamber 127 by using thetimer, the switching valve 190 is then switched into the firstconnection state, and then the bubble discharge mode is finished.

At that time, the inside pressure of the bellows 151 is raised by theworking fluid discharged from the pump chamber 127. But the bellows isdesigned so that the deformation due to the inside pressure issuppressed within an allowable range for elastic deformation. Further,the pump may be constructed so that a relief valve, not shown, isprovided in the bellows 151, and it is possible to suppress the insidepressure of the bellows 151 from being raised by opening the reliefvalve when the inside pressure of the bellows 151 is too high. Thus itis possible to maintain the inside pressure at a constant value of aboutone atmosphere or more in a gauge pressure and preferably a constantvalue between about one atmosphere and five atmospheres. In the bubbledischarge mode, the staying gas bubbles are excluded, so that it ispossible to recover the pump ability.

Next, a bellows pressing mode, which is performed to maintain the insidepressure of the bellows 151 to about one atmosphere or more in a gaugepressure and preferably a value between about one atmosphere and fiveatmospheres, will be described with reference to FIG. 8.

The inside pressure of the bellows 151 is detected by the pressuresensor 91 provided in the bellows 151. When the detected pressure issmaller than about one atmosphere in a gauge pressure, an instruction isgiven to the pressurizing mechanism 150 from the pump driving controlcircuit 180, so that the switching valve 190 is switched to the secondconnection state. Next, the diaphragm 60 is driven by the laminatedpiezoelectric element 70, so that the fluid is allowed to flow out ofthe pump chamber 127 to the outflow passage 128, similarly to thedischarge mode.

Then, the working fluid flows in the bellows 151 through the switchingvalve 182, so that the inside of the chamber formed out of the bellows151 is compressed. When the pump driving control circuit 180 confirms onthe basis of the detected value of the pressure sensor 91 that theinside pressure of the bellows 151 reaches about one atmosphere or morein a gauge pressure and preferably a value between about one atmosphereand five atmospheres, an instruction is given to the pressurizingmechanism 150 from the pump driving control circuit 180, the switchingvalve 190 is thus switched to the first connection state, and then thebellows pressing mode is finished. By performing this operation mode,even when leakage occurs in the switching valve 190, etc., the inside ofthe bellows 151 can be always maintained to the set pressure, so that itis possible to wait for the bubble discharge mode.

In the above fifth exemplary embodiment, the switching valve 190includes two valves. But an integrated three-way valve, etc. may beused. Since a hole (not shown in the figures), which can be airtightlyclosed, is provided in the bellows 151, it is possible to discharge thegas bubbles through the hole when too many gas bubbles are gathered inthe bellows 151.

In a modified example of the above fifth exemplary embodiment, in a casewhere the relationship between the time and the amount of leakage fromthe bellows 151 is known, the bellows pressing mode may be performedevery predetermined time interval without providing the pressure sensor91 in the bellows. In this case, by converting the amount of leakagefrom the time until the current bellows pressing mode is started afterthe previous bellows pressing mode is finished, it is possible to drivethe laminated piezoelectric element 70 for the time required to allowthe working fluid having the same volume as the amount of leakage toflow into the bellows 151 from the pump chamber 127.

Furthermore, by providing a relief valve, not shown, in the chamberformed out of the bellows 151 without providing the pressure sensor 91,the bellows pressing mode may be performed every predetermined timeinterval. As a result, if the inside of the bellows 151 is compressedabove the pressure set with the relief valve when the bellows pressingmode is performed, the relief valve is opened. Thus the working fluid isleaked, so that it is possible to maintain the inside of the bellows 151at a constant pressure.

In the above description, the pressure sensors described in the fourthexemplary embodiment can be similarly used as the pressure sensor 90 inthe pump chamber 127 to detect the inside pressure of the pump chamber127 and the pressure sensor 91 in the bellows 151.

Therefore, according to the fifth exemplary embodiment, the pressurizingmechanism 150 is provided with the passage switching device to switchbetween the first mode in which the working fluid flowing out of thepump chamber 127 is introduced into the chamber of the bellows 151 andthe second mode in which the chamber of the bellows 151 is shut off fromthe flow of the working fluid flowing out of the pump chamber 127. As aresult, it is possible to surely compress the working fluid in the pumpchamber 127 with the elastic force of the elastic member constitutingthe variable-volume chamber.

Furthermore, since the pressure sensor 91 to detect the inside pressureof the variable-volume chamber is provided, it is possible to controlthe inside pressure of the variable-volume chamber within a properpressure range. Furthermore, since the pressure sensor 90 is provided inthe pump chamber 127, it is possible to determine whether the gasbubbles stay in the pump chamber 127.

Furthermore, since the pressure applied from the pressurizing mechanism150 is set to a value between about one atmosphere and five atmospheresin a gauge pressure, it is possible to reduce the volume of the gasbubbles staying in the pump chamber as small as possible to discharge,without damaging the constituent components of the pump due to thepressure.

Sixth Exemplary Embodiment

Next, a pump according to a sixth exemplary embodiment of the presentinvention will be described with reference to FIGS. 10 and 11.

The sixth exemplary embodiment of the present invention has a basicstructure similar to the above fourth exemplary embodiment except forthe pressurizing mechanism, and thus differences therebetween will bedescribed in detail. The pump according to the sixth exemplaryembodiment is used without connecting an external tube to the outflowpassage 128, has a structure not requiring the switching valve (seeFIGS. 7 and 9) described in the fourth and fifth exemplary embodiments,and is characterized in that the pressurizing mechanism 150 is provideddetachably from the outflow passage 128.

FIG. 10 shows a vertical cross-sectional schematic of the independentpressurizing mechanism according to the sixth exemplary embodiment. InFIG. 10, the pressurizing mechanism 150 includes the bellows 151 and avalve case 153 to which the bellows 151 is fixed and receives a valve156.

As described in the above fourth exemplary embodiment, thevariable-volume chamber in which the working fluid stay and an openingportion 152 are formed in the bellows 151, which is closely fixed to anend of the valve case 153.

The valve case 153 includes the opening portion 152 communicating withthe bellows 151, an entry hole 155 into which the outlet connection tube131 (see FIG. 11) of the pump 100 is inserted, a valve fitting hole 154which communicates with the opening portion 152 and an entry hole 155and to which the valve 156 is fitted, and a rod inserting hole 160 intowhich a rod 159 of the valve 156 is inserted. A seal member 165 toprevent the working fluid from being leaked from the connected portionof the outlet connection tube 131 and the entry hole 155 is fitted intoan intermediate portion of the entry hole 155.

The valve 156 is connected to the rod 159 with the rod inserting hole160 therebetween and a washer 157 to fix the rod 159. Through-holes 158through which the working fluid passes are formed in the washer 157. Inaddition, a coil spring 161 to apply force to the valve 156 in order toseal the rod inserting hole 160 is provided between the washer 157 andthe inside wall of the entry hole 155.

The variable-volume chamber of the bellows 151 is compressed within arange of about one atmosphere to five atmospheres in a gauge pressure bymeans of the elastic force of the bellows 151, similarly to the fourthand fifth exemplary embodiment.

FIG. 11 is a partially vertical cross-sectional schematic illustrating astate where the above pressurizing mechanism 150 is fitted into theoutlet connection tube 131 of the pump 100. In FIG. 11, the entry hole155 of the pressurizing mechanism 150 is inserted into the outletconnection tube 131. At that time, the front end portion of the outletconnection tube 131 comes in contact with the washer 157 and compressesthe coil spring 161, so that the valve 156 is moved to a position toopen the rod inserting hole 160. At that time, the outflow passage 128and the chamber surrounded with the bellows 151 communicates with eachother, so that the working fluid can flow through the through-holes 158therebetween.

Next, a case where the gas bubbles do not stay in the pump 100 accordingto the sixth exemplary embodiment will be described. This case will bedescribed with reference to FIGS. 10 and 11.

In a normal state where the gas bubbles do not stay in the pump 100according to the sixth exemplary embodiment, the pressurizing mechanism150 is separated from the outflow passage 128 to discharge the workingfluid from the outflow passage 128. In this case, a principle ofdischarging the working fluid to the outflow passage 128 is similar tothat of the first exemplary embodiment. Therefore, when the gas bubblesstay in the pump chamber 127, increase in pressure of the pump chamberis hindered and the pump ability is thus deteriorated largely, so thatit is important to rapidly exclude the gas bubbles.

Next, a case where the gas bubbles stay in the pump chamber 127 will bedescribed.

When the gas bubbles stay, the outflow amount of the working fluid fromthe outflow passage 128 is decreased largely. Therefore, when a userobserves the decrease of the outflow amount from the outflow passage128, the user fits the pressurizing mechanism 150 into the outletconnection tube 131 (see FIG. 11). In FIG. 11, by pressing the washer157 with the end portion of the outlet connection tube 131 by a forcelarger than the elastic force of the coil spring 161, the coil spring161 is contracted, the valve 156 is thus opened, and the through-holes158 for the working fluid provided in the washer 157 and the openedvalve 156 communicate with each other, so that the outflow passage 128is connected to the inside (the chamber) of the bellows 151.

In this way, since the volume of the gas bubbles staying in the pumpchamber 127 is reduced by means of compression of the inside of the pumpchamber 127, the staying gas bubbles can be discharged into the bellows151 from the outflow passage 128, as described in the fourth and fifthexemplary embodiments. At that time, a lock mechanism to prevent theconnection of the outflow passage 128 and the bellows 151 from goingamiss may be provided.

In this exemplary embodiment, the inside pressure of the bellows may besuppressed from being raised by providing a relief valve in the bellows151. Furthermore, by providing a hole that can be airtightly closed inthe bellows 151, the gas bubbles staying in the bellows can bedischarged.

Therefore, according to the sixth exemplary embodiment, since thepressurizing mechanism is freely detachable, when the pressurizingmechanism is fitted into the outlet passage, the outlet passage and thepressurizing mechanism communicate with each other. The inside pressureof the variable-volume chamber is raised, thereby discharging the gasbubbles in the pump chamber. When the gas bubbles do not stay in thepump chamber, by separating the pressurizing mechanism, it is possibleto realize a small and light pump.

Seventh Exemplary Embodiment

Next, a pump according to a seventh exemplary embodiment of the presentinvention will be described with reference to FIGS. 12 to 14. Theseventh exemplary embodiment has the same basic structure and dischargeoperation of working fluid as the first to sixth exemplary embodimentsdescribed above, but is different from them in that a heating section isprovided as the bubble excluding device of the pump chamber.

Therefore, a relationship between the heating section and the bubbleexclusion will be described in detail.

FIG. 12 shows a vertical cross-section of the pump 200 according to theseventh exemplary embodiment. In FIG. 12, the pump 200 includes acup-shaped case 50 to which a laminated piezoelectric element 70 isfixed, an inflow passage 221 to introduce a working fluid, an outflowpassage 228 to discharge the working fluid, a pump case 220 having apump chamber 227, and a ring-shaped heater 212 provided in the pumpchamber 227.

In the case 50, one end portion of the laminated piezoelectric element70 is fixed to the inside bottom portion, and a diaphragm 60 is fixed toboth of the edge portion of the case 50 and the other end portion of thelaminated piezoelectric element 70. The pump case 220 is airtightlyfixed to the top surface of the diaphragm 60. The pump chamber 227 isformed in a space between the diaphragm 60 and the bottom portion of thepump case 220.

The inflow passage 221 and the outflow passage 228 are formed toward thepump chamber 227. In the inflow passage 221, a check valve 222 as afluid resistance element to open and close the inflow passage 221 isprovided at a connecting portion with the pump chamber 127. A part ofthe outer circumference of a cylindrical portion constituting the inflowpassage 221 functions as an inlet connection tube 230 to be connected toan external tube, not shown. A part of the outer circumference of acylindrical portion constituting the outflow passage 228 functions as anoutlet connection tube 231 to be connected to an external tube, notshown. Here, as the external tubes, not shown, for example, tubes madeof silicon rubber can be used.

Here, the inflow passage 221 itself is defined as an inlet passage. Theoutflow passage 228 itself is defined as an outlet passage. In arelationship of inertance values, as described above, the resultantinertance value of the inlet passage side is set to be smaller than theinertance value of the outlet passage side.

A ring-shaped heater 212 is fixed to the outer circumferential comerportion of the inside top wall of the pump chamber 227. The heater 212is airtightly inserted and fixed to the comer portion of the top wall ofthe pump chamber 227, so that the heater is not protruded from the topwall surface of the pump chamber 227 toward the pump chamber.

FIG. 13 is a schematic of the pump case 220 shown in FIG. 12 as seenfrom the pump chamber side.

In FIG. 13, the heater 212 is arranged at a position in the comerportion of the pump chamber 227 where gas bubbles easily stay. Theheater 212 is formed by fixing a resistance member to a ceramicssubstrate of alumina, etc., and then coating an insulating film thereon.Various members may be used as the resistance member. But members havinga high melting point, specifically, platinum or platinum alloy, may beused. Although not shown, a lead wire to supply power to the heater 212is drawn out through the pump case 220.

The inside of the pump chamber 227 is provided with a pressure sensor90, not shown (see FIG. 15).

Next, a modified example of the heater 212 according to the seventhexemplary embodiment will be described with reference to FIG. 14.

In FIG. 14, the heater 212 is formed as a thin plate having a circularplate shape, and is fixed to a wide range of the top wall surface of thepump chamber 227 other than the circumferential portion of the inflowpassage 221 and outflow passage 228. The heater 212 is inserted into thetop wall of the pump chamber 227 so that it is not protruded from thetop wall surface.

Next, a case where the pump 200 according to the seventh exemplaryembodiment is driven in a discharge mode of the working fluid will bedescribed.

The discharge mode is a mode in which power is not supplied to theheater 212 and a voltage is applied only to the piezoelectric element70. Since the discharge mode has been described in the first to sixthexemplary embodiments described above, the description thereof will beomitted. At that time, as described above, when the gas bubbles stay inthe pump chamber 227, the inside pressure of the pump chamber isdecreased and the pump ability is deteriorated, so that a bubbledischarge mode is performed.

Next, a case where the pump 200 according to the seventh exemplaryembodiment is driven in the bubble discharge mode will be described withreference to FIG. 15 (also, see FIG. 12).

FIG. 15 is a schematic of a driving circuit system of the pump 200. InFIG. 15, the driving circuit system of the pump 200 includes a pressuresensor 90 as a pressure detecting device in the pump chamber 227, aheater 212, a power distribution circuit 265 to control the heater 212,and a pump driving control circuit 280 to control the driving of thepump 200.

In a case where the maximum inside pressure of the pump chamber detectedby the pressure sensor 90 when the pump 200 is driven in the dischargemode is smaller, specifically by 50% or less, than the maximum insidepressure of the pump chamber when the pump is normally driven, the pumpdriving control circuit 280 determines that the gas bubbles stay in thepump chamber 227, and thus switches the driving mode to the bubbledischarge mode from the discharge mode. Then, the pump driving controlcircuit 280 sends a signal to the power distribution circuit 265. Thenthe power distribution circuit 265 starts the power distribution to theheater 212 in response to the signal.

Since the heater 212 is arranged at the comer portion in which the flowis stagnated and the gas bubbles easily stay as described above, thestaying gas bubbles existing in the vicinity thereof are heated by theheater 212, so that it is possible to expand the volume of the gasbubbles. As a result, if the size of the staying gas bubbles is notreceived in the stagnated area completely, the staying gas bubbles aremoved along the flow inside the pump chamber 227 due to the driving ofthe diaphragm 60 and thus can be discharged out of the outflow passage128. The bubble discharge mode is set to be finished after apredetermined time interval.

At that time, in a case where a plurality of heaters 212 are provided,by constructing the power distribution circuit 265 to sequentiallyswitch the power distributions to the respective heaters with time, thedistributed current can be reduced without change of the heat quantityof the heaters supplied with electricity, so that the power distributioncircuit 265 can be miniaturized.

By generating a heat quantity with which the working fluid existing onthe surface of the heaters 212 changes its phase, the gas bubbles due tothe phase change may be generated from the respective surface portionsof the heaters 212. In this method, the working fluid corresponding tothe volume of the generated gas bubbles is discharged to the outflowpassage 228. When the power distribution to the heaters 212 is stoppedand the change of phase is finished, the working fluid having an amountcorresponding to the volume of the discharged working fluid isintroduced into the pump chamber 227 through the check valve 222 fromthe inflow passage 221. At that time, since the gas bubbles due to thechange of phase are generated from the respective surface portions ofthe heaters 212, the flow inside the pump chamber 227 is complex and notstagnated, so that it is possible to discharge the staying gas bubblesgathered at the comer portions of the pump chamber which is thestagnated area in the discharge mode.

Furthermore, by generating a heat quantity enough to allow the workingfluid existing on the surface of the heater 212 to reach an overheatedstate through the power distribution from the power distribution circuit265, a film boiling such that a film-shaped gas bubble is generated fromthe whole surface of the heater 212 may be caused. In this method, sincethe volume of the gas bubbles generated due to the change of phase isincreased and the volume of the working fluid discharged to the outflowpassage 228 from the pump chamber 227 with one power distribution isincreased, it is easy to discharge the gas bubbles.

FIG. 16 shows a modified example of the heater 212. In FIG. 16, theheater 212 includes two of a heater 213 arranged at the inflow passage221 side and a heater 214 arranged at the outflow passage 228 side.

At that time, the phases of the distributed current to the respectiveheaters are deviated by using the power distribution circuit 265 (seeFIG. 15). As a result, after the inside pressure of the gas bubblesgenerated through the film boiling on the surface of one heater exceedsthe maximum value, the inside pressure of the gas bubbles generatedthrough the film boiling on the surface of the other heater reaches themaximum value.

Furthermore, it is preferable that the heater 213 close to and theheater 214 far from the opening portion of the pump chamber 227 of theoutflow passage 228 are provided, the power distribution to the farheater 214 is first started, and the power distribution to the heater213 is started later, so that the flow from the comer portion of thepump chamber 227 toward the outflow passage 228 can be easily generated.Of course, the number of heaters 212 may be two or more.

When the phase of the working fluid on the surface of the heater 212 ischanged, the diaphragm 60 may have any one of the stopped state and thedriven state. But it is preferable that the diaphragm 60 is driven, sothat the flow inside the pump chamber becomes complex and thus thestaying gas bubbles can be easily excluded.

In the seventh exemplary embodiment, the pump driving control circuit280 and the power distribution circuit 265 may be controlled so that theheater 212 is allowed to emit heat in a pulse shape by performing thepower distribution to the heater 212 using a pulse current. Thediaphragm 60 is driven in a direction in which the volume of the pumpchamber 227 is reduced in synchronism with the heat emitting.

As a result, it is possible to effectively discharge the gas bubblesstaying in the pump chamber while reducing the energy consumption of theheating section.

Furthermore, when the start and stop of the power distribution to theheater 212 are repeated several times during one bubble discharge mode,a more complex flow is generated inside the pump chamber. Thus, thestaying gas bubbles are more easily discharged. Furthermore, thedetected value by the pressure sensor 91 may be checked by driving thepump in the discharge mode after the bubble discharge mode is finished,so that it is possible to repeat the driving of the bubble dischargemode until the staying gas bubbles are discharged.

Therefore, according to the seventh exemplary embodiment, since theinside pressure of the pump chamber 227 is raised by providing theheater 212 inside the pump chamber 227 and thus the volume of the gasbubbles is compressed, it is possible to discharge the gas bubbles inthe pump chamber 227.

Furthermore, since the heater 212 is fitted into the wall of the pumpchamber 227 so that the heater is not protruded from the wall, and theheater is arranged at least at the comer portion of the pump chamber227, the gas bubbles can be prevented from staying in a protrudedportion in which the gas bubbles is easily stagnated. It is alsopossible to discharge the staying gas bubbles at the comer portion ofthe pump chamber 227.

Furthermore, when a plurality of heaters 212 are provided, it ispossible to reduce the quantity of energy per unit time to be suppliedto the heaters 212, and to rapidly discharge the staying gas bubbleswhile preventing the destruction of the pump.

Furthermore, since the pressure sensor 90 is provided in the pumpchamber 227, it is possible to determine whether the gas bubbles stay inthe pump chamber 227, thereby discharge the gas bubbles in the pumpchamber 227 as described above.

Furthermore, since the heater 212 emits heat in a pulse shape and thediaphragm 60 is driven in synchronism with the pulse, it is possible toeffectively discharge the gas bubbles staying in the pump chamber 227while reducing the energy consumption of the heater 212.

Furthermore, by performing the heating process to generate the heatquantity with which the working fluid in contact with the heater 212changes its phase, the gas bubbles due to the change of phase isgenerated in the pump chamber 227, so that the complex and non-stagnatedflow flowing toward the outflow passage 228 can be caused in the pumpchamber 227. As a result, it is possible to discharge the gas bubblesstaying in the pump chamber 227.

Furthermore, in the above description, since the bubble discharge modeis performed when it is determined by the pressure sensor 91 that thegas bubbles stay, the bubble discharge mode is not performed wastefully.But the bubble discharge mode may be performed every predetermined timeinterval. In this case, since the pressure sensor 91 can be omitted, itis possible to simplify the structure.

Furthermore, in the above description, the construction that thepressure sensor as the pressure detecting device for the pump chamber isprovided in the pump chamber 227 has been described. But differentconstructions may be employed. In one different construction, forexample, the inside pressure of the pump chamber 227 may be calculatedby measuring the deformation of the diaphragm 60 with a strain gauge ora displacement sensor. Further, the inside pressure of the pump chamber227 may be calculated by measuring the deformation of the valve memberin a state where the check valve 222 is closed, with a strain gauge or adisplacement sensor. Furthermore, the inside pressure of the pumpchamber 227 may be calculated by measuring current to drive thepiezoelectric element 70 with a current sensor. Furthermore, byproviding a strain gauge in the piezoelectric element 70, the insidepressure of the pump chamber 227 may be calculated on the basis of thevoltage applied to the piezoelectric element 70 and the measured valueby the strain gauge. At that time, any type of strain gauges that detectthe quantity of deformation by using variation in resistance, variationin capacitance, or variation in voltage may be used as the strain gauge.

The shape of the diaphragm 60 is not limited to the circular shape.Further, the check valve 222 is not limited to the passive valve whichperforms the opening and closing due to the pressure difference of thefluid, but an active valve which can control the opening and closingwith different forces may be used as the check valve.

The present invention is not limited to the above exemplary embodiments,but the present invention includes modifications and enhancements.

In the seventh exemplary embodiment, for example, the resultantinertance value of the inlet passage side is smaller than the resultantinertance value of the outlet passage side, and the heater 212 as thebubble discharging device is employed in the small high-pressure pumphaving an inertia effect of the working fluid. However, the bubbledischarge device may be employed, for example, in a pump using aunimorph type diaphragm shown in FIG. 17.

FIG. 17 is a vertical cross-sectional schematic of the pump employingthe unimorph type diaphragm. In FIG. 17, constituent elements differentfrom the seventh exemplary embodiment will be described in detail. Thepump 200 includes a unimorph type diaphragm 260 as a diaphragm, andcheck valves 222, 242 as the fluid resistance elements provided in bothof the inflow passage 221 and the outflow passage 228. In FIG. 17, thediaphragm 260 is airtightly fixed to the edge portion of the cup-shapedcase 250. The plate-shaped piezoelectric element 71 is fixed to thesurface of the diaphragm 260 facing the case 250. The pump case 220 isairtightly fixed to the top of the diaphragm 260, and the pump chamber227 is formed between the diaphragm 260 and the pump case 220.

The inflow passage 221 and the outflow passage 228 communicate with thepump chamber 227. The check valve 222, as the fluid resistance element,is provided in the inflow passage 221. The check valve 242, as the fluidresistance element, is provided in the outflow passage 228. Theplane-shaped heater 212, as the heating section, is provided on the topwall surface constituting the pump chamber 227 of the pump case 220. Theheater 212 is airtightly fitted into the pump case 220, so that theheater is not protruded from the pump case 220 toward the pump chamber.

The shape and material of the heater 212, and the position in which theheater is fitted into the pump case 220 are similar to the seventhexemplary embodiment and the modified example of the seventh exemplaryembodiment. Thus descriptions thereof will be omitted.

The discharge mode of the pump will be described.

If a voltage is applied to the plate-shaped piezoelectric element 71,the diaphragm 260 is deformed to have a convex surface toward the pumpchamber 227 through the diametrical deformation of the plate-shapedpiezoelectric element 71. If the application of voltage is stopped, thediaphragm is restored to the original shape. In this pump, when thecheck valves 222 and 242 close the flow passage, the diaphragm 260 isdeformed in the direction in which the volume of the pump chamber 227 isdecreased by using the deformation of the diaphragm 226, therebypressing the liquid inside the pump chamber 227. If the inside pressureof the pump chamber 227 becomes higher than the downstream pressure ofthe check valve 242, the check valve 222 is opened. Thus the liquid isdischarged to the outflow passage 228.

Next, by deforming the diaphragm 260 in the direction in which thevolume of the pump chamber 227 is increased, the inside pressure of thepump chamber 227 is decreased. Then, the check valve 242 is firstclosed. If the inside pressure of the pump chamber 227 becomes lowerthan the upstream pressure of the check valve 222, the check valve 222is opened, so that the liquid is introduced into the pump chamber 227from the inflow passage 221. By repeating the above actions, the workingfluid is transferred.

By providing the heater 212 as the bubble discharge device in the pumphaving the above structure, it is possible to allow the gas bubblesinside the pump chamber to flow out, and to suitably maintain the insidepressure of the pump chamber, so that it is possible to secure theamount of working fluid to be discharged.

In the above exemplary embodiments, the diaphragms 60, 45 have acircular shape, but the shape is not limited to the circular shape.Further, the check valves 41, 42 are not limited to the passive valvesthat perform the opening and closing process due to the pressuredifference of the fluid, but active valves that can control the openingand closing process with different forces may be used as the checkvalves. Furthermore, any element may be used as the piezoelectricelement to drive the diaphragm 60, only if it can be contracted andexpanded. However, in this pump structure, since the piezoelectricelement and the diaphragm are connected to each other without adisplacement enlarging mechanism and thus the diaphragm can be driven ata high frequency, it is possible to increase the flow volume with a highfrequency driving by employing a piezoelectric element having a highresponse frequency as in the embodiments, so that it is possible torealize a small and high-power pump. Similarly, a super magneticdistortion element having a high frequency characteristic may beemployed. Different liquid, such as oil may be used as the workingfluid, in addition to water.

Therefore, according to the first to seventh exemplary embodimentsdescribed above, since the bubble discharging device is provided, it ispossible to provide a pump capable of discharging the gas bubbles andthus maintaining a discharging ability thereof, even when the gasbubbles stay in the pump chamber.

INDUSTRIAL APPLICABILITY

The pump according to aspects of the present invention can be applied tovarious industries requiring a small liquid transfer pump.

1. A pump, comprising: a pump chamber whose volume can be varied bydriving a piston or a movable wall; an inlet passage to allow a workingfluid to flow into the pump chamber; an outlet passage to allow theworking fluid to flow out of the pump chamber, a fluid resistanceelement to open and close at least the inlet passage, a resultantinertance value of the inlet passage being set to be smaller than aresultant inertance value of the outlet passage; and a bubbledischarging device to discharge gas bubbles remaining in the pumpchamber.
 2. The pump according to claim 1, the pump chamber including aprimary pump chamber which communicates with the outlet passage andwhose volume can be varied by driving a piston or a movable wall, and asecondary pump chamber which communicates with the inlet passage andfunctions as the bubble discharging device and whose volume can bevaried by driving a movable wall.
 3. The pump according to claim 2,further comprising: a primary pump chamber inlet passage to allow theworking fluid to flow into the primary pump chamber; a primary pumpchamber outlet passage to allow the working fluid to flow out of theprimary pump chamber; a secondary pump chamber inlet passage to allowthe working fluid to flow into the secondary pump chamber; and asecondary pump chamber outlet passage to allow the working fluid to flowout of the secondary pump chamber, the primary pump chamber inletpassage also functioning as the secondary pump chamber outlet passage.4. The pump according to claim 3, further comprising: a fluid resistanceelement to open and close the primary pump chamber inlet passage; afluid resistance element to open and close the secondary pump chamberinlet passage; and a fluid resistance element to open and close thesecondary pump chamber outlet passage, the fluid resistance element toopen and close the primary pump chamber inlet passage also functioningas the fluid resistance element to open and close the secondary pumpchamber outlet passage.
 5. The pump according to claim 2, the movablewall provided in the secondary pump chamber being a diaphragm in which apiezoelectric element is attached to at least one surface thereof, andthe secondary pump chamber and the diaphragm including a unimorph pumpor a bimorph pump.
 6. The pump according to claim 2, further comprising:a driving switch control unit to switch the driving between thesecondary pump chamber and the primary pump chamber.
 7. The pumpaccording to claim 5, a driving electrode and a detecting electrode areformed in the piezoelectric element.
 8. The pump according to claim 2,further comprising: a pressure detecting section to detect an insidepressure of the primary pump chamber.
 9. The pump according to claim 1,further comprising: a pressurizing mechanism serving as the bubbledischarging device to raise and maintain the pressure of the workingfluid existing in the pump chamber.
 10. The pump according to claim 9,the pressurizing mechanism, comprises: a variable-volume chamber and aflow passage to allow the variable-volume chamber and the outlet passageto communicate with each other.
 11. The pump according to claim 10, thevariable-volume chamber being formed of an elastic member.
 12. The pumpaccording to claim 10, the pressurizing mechanism, further comprises: avolume varying mechanism to apply a pressure to vary the volume of thevariable-volume chamber.
 13. The pump according to claim 9, thepressurizing mechanism, comprises: a passage switching section to switchbetween a first mode where the working fluid flowing out of the pumpchamber is introduced into the variable-volume chamber, and a secondmode where the working fluid flowing out of the pump chamber is isolatedfrom the variable-volume chamber.
 14. The pump according to claim 10,further comprising: a pressure detecting section to detect an insidepressure of the variable-volume chamber.
 15. The pump according to claim9, a pressure detecting device being provided in the pump chamber. 16.The pump according to claim 12, the inside pressure of thevariable-volume chamber, which is pressurized by the pressurizingmechanism, ranging from about one atmosphere to about five atmospheresin a gauge pressure.
 17. The pump according to claim 9, the pressurizingmechanism, comprises: a variable-volume chamber; a flow passagecommunicating with the outlet passage; and an opening and closing memberto open and close the flow passage, and the pressurizing mechanism beingdetachable from the outlet passage, and the variable-volume chamber andthe outlet passage being allowed to communicate with each other byfitting the pressurizing mechanism into the outlet passage.
 18. The pumpaccording to claim 1, a heating section serving as the bubbledischarging device being provided in the pump chamber.
 19. The pumpaccording to claim 18, the heating section being received inside thewall of the pump chamber, or being arranged in a comer portion of thepump chamber.
 20. The pump according to claim 18, a plurality of theheating sections being provided.
 21. The pump according to claim 18,further comprising: a pressure detecting section to detect an innerpressure of the pump chamber.
 22. The pump according to claim 18, whenthe piston or the movable wall is being driven, a heating signal beinginput to the heating section.
 23. The pump according to claim 18, apulse-shaped heating signal being input to the heating section, and thepiston or the movable wall being driven in synchronism with the heatingsignal.
 24. The pump according to claim 19, the heating section heatingthe working fluid to change the phase of the working fluid in contactwith the heating section.